The procedure of monitoring and analyzing uterine contractions, during both pregnancy and labor, yields significant information concerning the condition of the unborn child as well as the advancement of labor. Such a procedure is useful during both routine and difficult pregnancies (e.g., those that have increased risk to the health of the child), to systematically evaluate fetal stress. The monitoring procedure is also used when labor is induced. Information indicating distress during pregnancy, labor, and delivery will prompt remedial action, including caesarean delivery, which may save the child from harm and even death. Thus, contraction frequency, duration, intensity, and resting tone are now monitored as part of accepted, standard, obstetrical procedure.
One example of a sensing element used to assess stress is a tocodynamometer or tocotransducer. Tocodynamometers can sense uterine activity externally and non-invasively. The advantages offered by those devices have caused them to be widely used with fetal monitors. Tocodynamometers measure the hardness of the abdominal wall, which is an indication of uterine activity. The tocodynamometer is held adjacent to the patient's abdomen, usually by a belt-like device, in the vicinity of the fundus (the top of the uterus). The tocodynamometer is initialized by setting the recording level so that it is about 10-15 mmHg between contractions. The output of the device is transmitted to the fetal monitor through a pressure transducer, the transducer converting the pressure change information received from the tocodynamometer to an electrical signal that it delivers to the fetal monitor. While externally applied devices like tocodynamometers can provide sufficient information to enable a physician to treat the mother and child during labor and delivery, such devices may suffer large measurement errors, particularly when the environment has extraneous noise or the mother moves extensively. Therefore, a physician may want to have more accurate measurements than can be obtained using external monitoring devices, especially in those childbirth cases involving an elevated risk of complication.
To obtain more reliable and accurate information about the mother's uterine contractions, a physician will often invoke intrauterine pressure monitoring. Intrauterine devices provide information about the frequency, duration, intensity, and resting tone of the uterine contractions. More important, intrauterine devices reduce measurement errors relative to external devices because the uterine pressure is measured directly. However, intrauterine pressure-monitoring devices cause significant discomfort when inserted into the patient, are cumbersome to work with, result in inaccurate or difficult-to-obtain measurements, and/or are potentially dangerous in that the distal ends may dislodge while inside the patient and/or may perforate the uterus or amniotic sac.